1. Field of the Invention
The present invention relates to the field of high resolution analog-to-digital converters.
2. Prior Art
High-resolution Analog-to-Digital Converters (ADC's) often require some form of calibration to overcome the component mismatches inherent in the circuitry. A digital calibration technique has been published by Prof. Bang-Sup Song which is applicable to pipelined analog-to-digital converters ("Interstage Gain Proration Technique for Digital-Domain Multi-Step ADC Calibration", Lee et al., IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing, Vol. 41, No. 1, January 1994). It corrects for component mismatch as well as interstage gain errors (gain proration). According to the article by Bang-Sup Song, "a gain-error proration method is proposed, which distributes the full scale error of the latter stages evenly over the range so that the signal conversion range of the latter stages may match that of the former stages, thereby simplifying multiple-stage digital calibration and extending it to the general multi-step/pipelined architecture." Bang-Sup Song performs a capacitor non-linearity calibration first and then, if the calibrated stage is not the first stage, he performs gain proration. In this case, he does the gain proration twice. However, when the previous stage is then calibrated by the now calibrated subsequent stage(s), the calibration algorithm adjusts the gain of the previous stage so that the interstage gain error is corrected. If there were no roundoff errors, the explicit gain proration will not degrade performance. With roundoff errors, it is believed that the explicit gain proration will degrade performance.
The present invention recognizes that this "gain proration" is not necessary as part of the calibration, but rather that it can be "built in" to the device mismatch corrections. On average, it is believed that in comparison, the gain-proration will degrade the performance of the calibrated analog-to-digital converter and increase the calibration time.